My invention relates generally to the art of data recording on tape media, and particularly to apparatus for the recording and reproduction of digital data on multitrack magnetic tapes packaged in cassette form or otherwise preloaded in similar reel to reel envelopes. More particularly, my invention pertains to a method and means in such apparatus for positioning a data transducer or head in a transverse reference position on one edge of the tape in order to enable control over the subsequent transverse head location with respect to a plurality or multiplicity of parallel record tracks on the tape.
Multitrack magnetic tapes have found widespread acceptance as compact and inexpensive data storage media. Such a tape permits digital data to be recorded thereon along a plurality or multiplicity of tracks extending side by side in the longitudinal direction of the tape. Normally, each track is recorded in a direction opposite to that in which the preceding track has been formed. The result is what is known as a serpentine track pattern.
The record tracks of such a serpentine multitrack tape may be individually identified by coded data prerecorded on each such track. Alternatively, in the absence of such track identification data, the head may be positioned transversely of the tape by first precisely locating the head on one edge of the tape to provide a reference head position. The head may then be accessed from this reference position to a desired track location on the tape.
U.S. Pat. No. 4,422,111 to Moeller et al. describes and claims the second mentioned type of head positioning system. It teaches the use of a magnetic tape having prerecorded thereon a plurality of longitudinally readable key patterns of equal length each extending across the entire width of the tape. The key patterns are separated from one another by recordable tape sections of greater equal length, with each pattern uniquely identifying an adjacent record section. These key patterns are also utilized during initial loading operations to determine the precise edge of the tape and thereby provide a reference head position from which all subsequent track locations may be indexed.
Thus, as far as I am aware, the positioning of the head in the transverse direction of a multitrack magnetic tape has conventionally been accomplished by prerecording track identification data or key patterns on the tape. I object to such prerecording of identification data or patterns on magnetic tapes because they require special recording equipment, which has added substantially to the manufacturing costs of the tapes. Also, such prerecorded tapes impose restrictions on their latitude of use. The teachings of Moeller et al. have the additional disadvantage that, since the tape edge is detected by comparison of the output from the playback head, traveling across the width of the tape for reading a key pattern, with a predetermined threshold level, difficulties have been encountered in the determination of this threshold level.